Voter trust in national institutions is "crumbling into dust", according to Lord Ashdown.

The former Liberal Democrat leader, who is running the party's 2015 election campaign, says he fears a series of scandals has contributed to declining faith in politicians, journalists, bankers, the BBC and NHS, which could push people into the arms of "demagogues" such as Ukip's leader, Nigel Farage.

"I'm reminded of the terrible line in Larkin: 'England, with a cast of crooks and tarts.' Now I'm not saying that's true. [But] I think all of these add up to a mood of Jacobinism which I think is quite frightening" he told the Times. "If this is the age of the collapse of beliefs, the dissolution of institutions, then what you're going to find is people who find an appeal in answers that are simplistic."

Some of Ashdown's harshest criticism was reserved for the BBC and NHS, two of the UK's traditionally most treasured national instutitions. "The BBC is revealed as an organisation which can't manage its own affairs, misspends public money and seems to have been complicit in aggrandising someone [Jimmy Savile] whose proclivities would be rejected by most people.

"The NHS, we are told, is to be failing right down to the level of doctors. Nurses were angels but some turn out to be witches."

While not predicting further riots, Ashdown also said that he was surprised that Britain has got through the recession with so little street protest. "I don't predict them and I don't want them – and I don't want to be scaremongering. But there is something very unsettling out there.

"I cannot exclude the possibility that we'll see people who don't believe they can make their point within the political system making their point on the street instead."

Ashdown said voter disaffection could have a radical impact on the general election next year. "We are all proceeding on the basis that the next election will be a conventional election. I'm not entirely certain that if the leviathan lying below the surface decides to swish its tail, that's necessarily the case."

The research found anger with the political class and broken promises made by high-profile figures that most rile voters, rather than boredom with Westminster.

Earlier this week, Sarah Teather, the Libl Dem former children's minister, also warnedspoke about some of the reasons for declining trust in politicians. She said ministers have become caught up in a "cycle of democratic self-harm" in which they spent too much time "flapping around trying to be relevant" and responding to imaginary problems in the hope of pleasing the public.

"We get ourselves into our own little spiral. We end up inventing problems to pretend we're relevant, and then try to fix the problems we've just invented. The EU migration stuff is a classic example.

"The public know it's guff, so their trust in politicians goes down. And then our anxiety about not being relevant goes up, so we kind of get into a cycle of democratic self-harm, so we get progressively more frenzied about chasing wilder and wilder straw men and the public get more and more cynical. I'm not convinced that's the best way of demonstrating we're in touch."

•This article was amended on Friday 3 January 2014 to correct the spelling in the standfirst.